"Mercury (Hg) is a global environmental contaminant that is deposited from the atmosphere and converted to methyl mercury (MeHg) in aquatic ecosystems. Historically Hg was thought to pose a risk to aquatic but not terrestrial wildlife. Recent studies have found that MeHg can be transported via emergent aquatic insects to terrestrial ecosystems. Tetragnathid spiders are a key link between aquatic and terrestrial ecosystems because they consume emergent aquatic insects and are themselves consumed by songbirds. I studied spatial patterns in MeHg concentration in tetragnathid spiders at Caddo Lake, Texas/Louisiana, USA. I then used MeHg concentrations in spiders to estimate the potential risk to arachnivorous songbirds. At 89% of the 56 sampling sites, Hg concentrations in spiders were high enough to pose a risk to chickadee nestlings. This study suggests that terrestrial spiders that consume aquatic insects accumulate levels of MeHg that could pose a risk to songbirds at Caddo Lake"--Abstract.